Increasing cost of fossil fuel and environmental concerns have stimulated worldwide interest in developing alternatives to petroleum-based fuels, chemicals, and other products. Biomass materials are a possible renewable alternative to petroleum-based fuels and chemicals.
Lignocellulosic biomass includes three major components. Cellulose, a primary sugar source for bioconversion processes, includes high molecular weight polymers formed of tightly linked glucose monomers. Hemicellulose, a secondary sugar source, includes shorter polymers formed of various sugars. Lignin includes phenylpropanoic acid moieties polymerized in a complex three dimensional structure. The resulting composition of lignocellulosic biomass is roughly 40-50% cellulose, 20-25% hemicellulose, and 25-35% lignin, by weight percent.
Very few cost-effective processes exist for efficiently converting cellulose, hemicellulose and lignin to components better suited for producing fuels, chemicals, and other products. This is generally because each of lignin, cellulose and hemicellulose demands distinct processing conditions, such as temperature, pressure, catalysts, reaction time, etc., in order to effectively break apart their polymer structure. Because of this distinctness, most processes are only able to convert specific fractions of the biomass, such as cellulose and hemicellulose, leaving the remaining fractions behind for additional processing or alternative uses.
Hot water extraction of hemicellulose from biomass, for example, has been well documented. The sugars produced by hot water extraction are however unstable at high temperatures leading to undesirable decomposition products. Therefore, the temperature of the water used for hot water extraction is limited, which can reduce the effectiveness of the hot water extraction.
Studies have also shown that it is possible to convert microcrystalline cellulose (MCC) to polyols using hot, compressed water and a hydrogenation catalyst (Fukuoka & Dhepe, 2006; Luo et al., 2007; and Yan et al., 2006). Typical hydrogenation catalysts include ruthenium or platinum supported on carbon or aluminum oxide. However, these studies also show that only low levels of MCC are converted with these catalysts, and selectivity toward desired sugar alcohols is low.
APR and HDO are catalytic reforming processes that have recently shown to be promising technologies for generating hydrogen, oxygenates, hydrocarbons, fuels, and chemicals from oxygenated compounds derived from a wide array of biomass. The oxygenated hydrocarbons include starches, mono- and poly-saccharides, sugars, sugar alcohols, etc. Various APR methods and techniques are described in U.S. Pat. Nos. 6,699,457; 6,964,757; 6,964,758; and 7,618,612 (all to Cortright et al., and entitled “Low-Temperature Hydrogen Production from Oxygenated Hydrocarbons”); U.S. Pat. No. 6,953,873 (to Cortright et al., and entitled “Low-Temperature Hydrocarbon Production from Oxygenated Hydrocarbons”); and U.S. Pat. Nos. 7,767,867; 7,989,664; and U.S. Patent Publication No. 2011/0306804 (to Cortright, and entitled “Methods and Systems for Generating Polyols”). Various APR and HDO methods and techniques are described in U.S. Pat. Nos. 8,053,615; 8,017,818; 7,977,517; and U.S. Patent Publication Nos. 2011/0257448; 2011/0245543; 2011/0257416; and 2011/0245542 (all to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); U.S. Patent Publication No. 2009/0211942 (to Cortright, and entitled “Catalysts and Methods for Reforming Oxygenated Compounds”); U.S. Patent Publication No. 2010/0076233 (to Cortright et al., and entitled “Synthesis of Liquid Fuels from Biomass”); International Patent Application No. PCT/US2008/056330 (to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); and commonly owned co-pending International Patent Application No. PCT/US2006/048030 (to Cortright et al., and entitled “Catalyst and Methods for Reforming Oxygenated Compounds”), all of which are incorporated herein by reference.
One drawback of catalytic technologies is the possible negative effects of water, contaminants, and other residual products on the performance of the catalyst. For instance, ash components (e.g., calcium, aluminum, potassium, sodium, magnesium, ammonium, chloride, sulfate, sulfite, thiol, silica, copper, iron, phosphate, carbonate, and phosphorous), color bodies (e.g., terpenoids, stilbenes, and flavonoids), proteinaceous materials, and other inorganic or organic products from biomass conversion can interact with the catalyst to severely limit its activity. More complex polysaccharides, such as raw cellulose and hemicellulose, as well as lignin, and their complex degradation products, have also proven to be difficult to convert due to their size and inability to interact with the catalyst. Therefore, a process for generating fuels and chemicals and other hydrocarbons and oxygenated hydrocarbons from more complex biomass components would be beneficial. It would also be beneficial to improve the efficiency of such processes by minimizing the number of reaction steps, and thus reactors, necessary to perform the conversion process.